Fixed framerate definately allow replays and such be easier.

Lowering (display) framerate intentionally when explosions happen is a cool classical effect.

For multiplayer you can kinda have best of both worlds by having a seperate server "tick" rate and client display rate.

While it does become ruins you can get your old items back from the unsafe areas still through a series of time manpiulation quests.
3/3

Then there is a climax/crisis event where you can lose your "base" slot if you aren't active and if other players don't defend it.

You can retreive your stuff if you lose the slot in the "safe higher tax" area. It becomes ruins in the non safe area and content for other players.
2/3